1. Field of the Invention
This invention relates to an in situ method for producing debond coating on silicon carbide fibers to be incorporated in a composite and the resulting product.
2. Description of the Related Art
Current debond coatings are usually applied to fibers by chemical vapor deposition (CVD) or chemical vapor infiltration (CVI). These techniques are generally slow and costly. High temperatures, special atmospheres, special chemicals and special apparatus increase costs. Coatings sometimes contain defects due to touching fibers and incomplete spreading of fiber tows. Typical debond layer materials are carbon such as described by R. C. Loszewski in U.S. Pat. No. 5,024,889 and by H. Sakamoto in U.S. Pat. No. 5,055,430 and boron nitride as described by T. L. Jessen in U.S. Pat. No. 5,407,740 and R. Rice in U.S. Pat. No. 4,642,271. Special handling is generally used to prevent damage to the debond coatings. The ability to place a nickel coating on a fiber is shown by L. G. Morin in U.S. Pat. No. 4,942,090 on carbon fibers.
It is an object of this invention to control bonding between the fiber reinforcements and the matrix in composite materials.
It is a further object of this invention to improve composite properties by providing a debonding layer on fibers in ceramic matrix composites.
It is a further object of this invention to provide tailored debond layers which absorb energy and make for tougher composite materials.
It is a further object of this invention to provide improved, in situ produced debond coatings on silicon carbide fibers which may be used in composites to produce superior products.
It is a further object of this invention to provide debond coatings on silicon carbide fibers where there is an outer layer containing nickel silicide, Ni2Si, and carbon.
It is a further object of this invention to provide composite precursors where the composite forming material contains silicon carbide fibers with improved debond coatings.
These and further objects of the invention will become apparent as the description of the invention proceeds.
A debonding coating is formed on fibers, and especially silicon carbide fibers, by forming a thin film of a metal or metal silicon alloy on silicon carbide fibers and annealing the fibers at a temperature sufficient to produce an effective amount of a metal silicide and carbon to form a debond coating on the silicon carbide fibers. These fibers having the debond coating can be added to composite forming materials and the mixture can be treated to form a consolidated composite. A more preferred way to make the consolidated composite is to place the silicon carbide fibers with the initial metal film coating into the composite forming materials and then to heat the mixture to form the debond coating in situ on the fibers and to form the consolidated composite. Preferred heating techniques include high temperature annealing, hot-pressing, or hot isostatic pressing (HIP).